This project attempts to define the value and limitations of platelet survival time, and of platelet suppressant therapy in patients with rheumatic heart disease. We have shown that platelet survival time (autologous labelling with chromium-51) is shortened in most patients with rheumatic heart disease, in particular those with a history of systemic embolism. In the current study, patients with shortened platelet survival are randomized to treatment with either sulfinpyrazone or placebo and followed for four years. Patients with normal platelet survival are followed without specific therapy. At the present time 138 patients have been enrolled and embolism has occurred in eight. Of these eight, one was receiving sulfinpyrazone and seven were receiving placebo (X2 equals 4.31; NS). Sulfinpyrazone increased shortened platelet survival time, platelet survival was unaltered in the patients receiving placebo and in the untreated patients with normal platelet survival. It is anticipated that the trial will yield positive results suggesting that platelet survival is shortened in patients who have had or will have thromboembolism and that sulfinpyrazone will decrease the frequency of embolism.